Polyimides are known in the art for use in the manufacture of circuit assemblies such as chips (e.g. chip back end of line), multichip modules, and circuit boards. For example, Watanabe's U.S. Pat. No. 4,847,353 discloses the use of a large class of polyimides and copolymers of polyimides in the manufacture of circuit boards. Polyimides are useful in forming dielectric layers, passivation layers, alpha particle barriers and stress buffers. Polyimides are also useful as a dielectric material to insulate the conductor wiring interconnecting integrated circuit chips on a multichip module. A multichip module is an intermediate level of packaging between the chips and the circuit board. Multichip modules are made up of a plurality of insulating and conducting layers wherein the conducting power, signal and ground layers deliver power to the chips and distribute the input/output signals between chips on the module or to/from the circuit board. Multichip modules typically contain input/output pins on the bottom surface for connection to the circuit board.
Poly(4,4'-oxydiphenylene pyromellitimide) is a insulating polyimide polymer used in the manufacture of multichip modules and chips. However, in some cases, such as under high temperature and humidity, films comprising this polyimide will separate (lift off) from the substrate or underlying polymer layer. This separation causes defects or voids which can lead to corrosion and eventual electrical shorts or opens in the wiring. There still is a need in the art for a suitable polyimide having good physical, insulative and adhesion properties for use in making circuit assemblies.
It is therefore an object of the present invention to provide a circuit assembly comprising one or more layers of a polyimide having improved adhesion properties.